<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    @keyframes myfirst {
      0% {
        transform: rotate(0deg);
      }


      100% {
        transform: rotate(360deg);
      }
    }

    .a {
      background-color: aqua;
      height: 200px;
      width: 200px;
      animation: myfirst 3s linear infinite;
    }
  </style>
</head>

<body>
  <div class="a">123</div>
</body>
<script>
</script>

</html>